Vehicle structural beam and method of manufacture

Abstract

A vehicle structural beam, such as a door intrusion beam, which possesses an elongate tubular beam part which at opposite ends is provided with mounting flanges for securement to a vehicle frame. The elongate tubular beam part and the flanges provided at opposite ends are defined by an integral, one-piece, monolithic steel structure which has been initially roll-formed from an elongate flat metal sheet to define the closed tubular structure of the tubular beam part, and which has been subjected to heating and quenching so that the elongate tubular beam part is of relatively high strength steel throughout its entire length, whereas the integrally and monolithically joined end flanges remain as lower strength steel which has been significantly unaffected by the heat treatment and quenching so as to permit appropriate shaping thereof and ease of welding to the vehicle frame.

What is claimed is:  
     
       1. An elongate structural beam for a vehicle, comprising; 
       (1) a one piece, monolithic, elongate structural member constructed of sheet steel;  
       (2) said one piece, monolithic, elongate structural member including:  
       (a) an elongate center beam part roll formed of said sheet steel and having a closed tubular cross section, and  
       (b) first and second flange parts located, respectively, at opposite ends of said elongate center beam part,  
       (3) the elongate center beam part being of high-strength steel formed by heat treating solely the elongate center beam part, and the flange parts being of low-strength steel permitting welded attachment to a frame.  
     
     
       2. The beam of  claim 1 , wherein the elongate center beam part has adjacent edges extending along the length thereof and welded together to define the closed tubular cross section. 
     
     
       3. The beam of  claim 2 , wherein each said flange part includes a flat plate-like portion which projects away from the respective end of the elongate center beam part in the lengthwise direction thereof. 
     
     
       4. The beam of  claim 3 , wherein each said flange part includes a second flat plate-like portion which is monolithically joined to and projects transversely relative to said first mentioned flat plate-like portion. 
     
     
       5. The beam according to  claim 2 , wherein the elongate center beam part is defined by a plurality of generally flat sides joined to define a generally trapezoidal cross-sectional shape, and wherein said flanges are monolithically and integrally joined directly to only one of said flat sides at opposite ends thereof. 
     
     
       6. The beam according to  claim 2 , wherein the elongate center beam part includes a pair of generally hollow box-like tube sections which extend lengthwise of the center beam part in generally parallel but sidewardly spaced relationship and which are joined by a generally flat base wall which extends between the hollow box-like tube sections and which also defines one of the side walls of said hollow box-like tube sections, and said flanges being monolithically and integrally joined directly to only said base wall at opposite ends thereof so that said flanges project outwardly away from said base wall beyond the respective ends of the elongate center beam part. 
     
     
       7. A vehicle impact beam according to  claim 5 , wherein the closed tubular cross section of said center beam part is generally trapezoidal and is defined by generally front and rear flat side walls joined together by a pair of generally flat edge walls which converge as they join to the rear side wall, and said flanges being integrally and monolithically joined to and projecting outwardly from solely said front side wall. 
     
     
       8. The beam of  claim 1 , wherein the beam is formed from a unitary, monolithic piece of low-strength steel sheet which is notched at predetermined intervals forming notched and un-notched portions; the un-notched portion of the sheet being formed into a closed tubular portion by fixedly connecting side edges of the un-notched portion; and only the un-notched portion being treated to strengthen only the tubular portion which defines the elongate center part of the beam. 
     
     
       9. The beam according to  claim 2 , wherein the beam is one of a door intrusion beam, a bumper beam and a roof beam, and wherein the flanges are welded to a vehicle frame. 
     
     
       10. A door intrusion beam for disposition within and attachment to a door frame of a vehicle, comprising an elongate, one-piece, monolithic structural beam member constructed of sheet steel and having an elongate roll-formed center beam part defining a closed tubular cross section, the structural beam member also having first and second flange parts respectively located at opposite ends of said elongate center beam part and integrally and monolithically joined thereto, said elongate center beam part being of heat-treated high strength steel, and said flange parts being of low strength steel to permit welded securement of the flanges to the door frame.